Friction welding apparatus

ABSTRACT

A friction welding apparatus is particularly adapted for the friction welding of relatively heavy workpieces, as for example the center section and wheel bearing end spindles of a drive axle housing, and comprises special hydrostatic bearing equipped devices for mounting the rotating workpieces. Each such device is mounted for axial displacement and comprises a rotatable arbor assembly to which the rotatable workpiece, such as a wheel bearing end spindle, is clutched and the arbor assembly is rotatably supported in a housing by two axially spaced hydrostatic journal bearings. Front and rear hydrostatic thrust bearings are provided between the arbor assembly and the housing. Oil under suitable pressure is supplied to both the journal and thrust hydrostatic bearings, and controls are provided for attaining and maintaining suitable fluid pressure levels at these bearings. One aspect of control insures that the workpiece is not secured to the arbor assembly until journal bearing oil pressure reaches a certain level. Oil is forced under high pressure into the bearings through specially arranged passages and after being discharged from the hydrostatic bearings returns to a sump at lowered pressure.

United States Patent Stamm [54] FRICTION WELDING APPARATUS [72]Inventor: Alex F. Stamm, Rochester, Mich.

[73] Assignee: North American Rockwell Corporation,

Pittsburgh, Pa.

[22] Filed: Oct. 1,1970

[21] Appl.No.: 77,208

Related U.S. Application Data V [62] Division of Ser. No. 650,505, June30, 1967, Pat. No.

[52] U.S. Cl .L ..279/4, 228/2, 308/9, 308/DIG. 13

[51] Int. Cl ..B23b 31/30, F166 7/04, B23k 27/00 [58] Field of Search..279/4; 308/9, DIG. l, DIG. 13; 228/2 [56] References Cited 7 UNITEDSTATES PATENTS 3,223,463 12/1965 Porath ..308/9 [is] 3,671,049 51 June20, 1972 Primary Examiner-Francis S. l-lusar Attorney-George R. Powersand Jdhn R. Bronaugh [57] ABSTRACT A friction welding apparatus isparticularly adapted for the friction welding of relatively heavyworkpieces, as for example the center section and wheel bearing endspindles of a drive rotatable arbor assembly to which the rotatableworkpiece,

such as a wheel bearing end spindle, is clutched and the arbor assemblyis rotatably supported in a housing by two axially spaced hydrostaticjournal bearings. Front and rear hydrostatic thrust bearings areprovided between the arbor assembly and the housing. Oil under suitablepressure is supplied to both the journal and thrust hydrostaticbearings, and controls are provided for attaining and maintainingsuitable fluid pressure levels at these bearings. One aspect of controlinsures that the workpiece is not secured to the arbor assembly untiljournal bearing oil pressure reaches a certain level. Oil is forcedunder high pressure into the bearings through specially arrangedpassages and after being discharged from the hydrostatic bearingsreturns to a sump at lowered pressure.

'10 Claims, 10 Drawing Figures PATENTEDJUN201Q72 3.671.049

sum 1 OF 7 FIG. I

ALEX F. STA/WM INVENTOR.

PATENTED JUN 2 0 I972 SHEET 3 BF 7 L INVHVTOR. ALEX F. STA MMPATENTEUJUREUISYZ 3.671.049

sum no; 7

INVENTOR. LEX 5 STA MM PATENTEDJUNZO m2 SHEET 5 OF 7 INVENTOR. ALEX FSTAMM PATENTEDJHH 20 1972 SHEET 6 OF 7 INVENTOR.

ALEX l-T STAMM SUMP FIG. 6

A TTOR/VE Y3 FRICTION WELDING APPARATUS This is a division of copendingapplication Ser. No. 650,505, filed June 30, 1967 and now US. Pat. No.3,575,334.

BACKGROUND AND SUMMARY OF INVENTION sitated when very heavy metal massessuch as steel drive axle housing components are brought together intorelatively rotating frictional engagement.

Standardized methods of. design of machinery for such heavy dutyfriction welding lead to the conclusion that the extremely heavy radialbearingloads to be encountered require relatively large cumbersome andexpensive conventional type journal bearings, and there has been no realevaluation of the nature of heavy duty thrust bearings which would beadequate except to realize that such bearings would have to'be verylarge and complex.

The invention solves these problems of space and adequacy byincorporatinghydrostatic bearings in combination into the machine, andthis is the major object of the invention.

A further object of the invention is to provide a hydrostatic bearingunit of entirely novel construction having a rotatable arbor assemblyadapted to be clutched to a workpiece to be rotatedand advanced intofriction welding engagement with a stationary workpiece, the arborassembly being radially supported on axially spaced hydrostatic journalbearings in a housing and having from and rear hydrostatic thrustbearing supports in the housing. More detailed objects of the inventioninclude in combination special oil passagearrangements to the respectivebearings, a control systemfor oil flow and pressure, and theincorporation in the arbor assembly of a fluid pressure responsivepiston actuating the workpiece attachment clutch.

While hydrostatic bearings per se are known and used, the inventionrepresents a novel arrangement thereof and in combination with othercomponents of the friction welding apparatus, as will appear.

BRIEF DESCRIPTION or DRAWINGS FIG. 1 is a top plan view illustrating thearrangement of parts in apparatus incorporating a preferredembodiment'of the invention;

FIG. 2 is a generally perspective view showing a hydrostatic 1 ficeconstruction for delivering oil to the front thrust bearing. shown inFIG. 3;

FIG. 4 is a sectional view substantially along line 4-4 of FIG. 3;

FIG. 4A is an enlarged fragmentary view of one of the journal bearingoil supply orifice structures shown in FIG. 4;

FIG. 5 is a sectional view substantially along line 5-5 of FIG. 3; I

FIG. 6 is a diagrammatic view showing the circuit arrangements forexplanation of operation under the invention.

FIG. 7 is an enlarged fragmentary elevation of the outboard end of theleft-hand bearing unit and illustrates details of the belt and pulleymotor-driven connection for rotating a workpiece carried by the unit;and

FIG. 8 is an elevation similar to FIG. 7 and illustrating the outboardend of the right-hand unit of FIG. 1.

PREFERRED EMBODIMENTS FIG. 1 illustrates a friction welding apparatuswherein three workpieces ll, 12 and 13 are adapted to be friction weldedtogether. In this arrangement the central workpiece 12, which may be anaxle housing center section, is held stationary and the other twoworkpieces, which may be wheel bearing end spindles l1 and 13, arerotated while being moved into contact with opposite ends of workpiece12.

The central workpiece 12 is mounted in a cradle structure 14 whereinopposite sides are engaged and held suitably by adjustable jaws l5 and16. The oppositely extending arms of workpiece 12 are clamped tightly insimilar fixtures 17 each of which has opposed adjustable jaws indicatedat 18 and 19 for gripping the workpiece. This arrangement supports andanchors workpiece 12 against rotation or axial displacement. Cradle 14is secured rigidly to the machine base 21 during operation. v

workpiece 11 is mounted upon a hydrostatic bear-ing unit carrier 22 andworkpiece 13 is mounted upon a similar hydrostatic bearing unit carrier23 at opposite ends of base 21. These carriers 22 and 23 and the bearingunits on them are essentially the same.

FIG. 2 shows carrier 23 as comprising an annularfframe 24 having rigidside members 25 and 26 formed at their lower ends with parallelrectangular guideway grooves 27 and 28 respectively slidably fittingwith parallel rails 29 and 31 on the machine base 21.

A pair of power cylinders 32 and 33 are fixed on base 21 with theirpiston rods 34 and35 respectively projecting parallel and at the samelevel into rigid connection with carrierframe 24. Fasteners such as nuts36 assure that piston rods 34 and 35 are unitarily secured to frame 24.As will appear in troduction of fluid under pressure into both cylinders32 and 33 will advance the carrier and the bearing unit cartridge 37thereon toward the stationary workpiece 12.

A shaft 38, located centrally of carrier; 23 and midway betweencylinders 32 and 33, hasa splined section 39 which axially slidably butnon-rotatably extends through the hub of an axially stationary pulley 40(see FIG. 8). A belt 41 connects pulley 40 to a pulley 41a fixedlymounted on an idler shaft 41b that is suitably journalled for rotationabout an axis extending parallel to and vertically below shaft 38. Apulley 41c is also fixedly mounted on shaft 41b and a belt 42 FIG.-l)connects pulley 410 to a pulley 43 on the output shaft 44 of a powerassembly 45 consisting essentially of an electric motor 46 connected toshaft 44 through a clutch unit at 47 and having a braking unitassociated therewith at 48.

Referring to FIG. 8, a sleeve or spindle 40asecured to the machine frameas by screws 40b and coaxially surrounds shaft 38 so as to permit freesliding of the shaft therethrough. Sleeve 40a is formed with axiallyspaced cylindrical sections 400 and 40d on which are mounted the innerraces of tapered roller bearing units 40e and 40f respectively. Theouter races of the bearing units axially abut internal annular shoulders40g and 40h respectively of pulley 40. The outer end of the internalrace of bearing unit 40f abuts axial shoulder 40] on the sleeve. Theouter end of the sleeve is threaded at 40k to mount a locknut assembly40m which abuts the outer end of the inner race of bearing unit 40e.When .the locknut assembly is tightened the bearings are preloaded andretained, and as shown these bearing units 40e and 40f also act asthrust bearings for preventing axial displacement of pulley 40 witrespect to shaft 38. I

An axially aligned drive collar 40n is secured to pulley 40 as by screws40p and has an internally splined hub 40q meshed with shaft splines 39.Shaft 38, during operation when the carrier 23 is displaced along theframe, slides axially through collar 40;: while retaining drive betweenshaft 38 and pulley 40 without axial displacement of the pulley.

Shaft 38 enters the hydrostatic bearing unit cartridge 37 v wherein aswill appear it may be operably drive connected to the inserted workpieceBy confining pulley 40 against axial displacement and by providing thesplined drive connection between pulley and shaft 38, continuousrotation of shaft 38 need not be interrupted as the carrier for thecartridge is axially displaced along guide rails 39 and 31.

As shown in FIG. 8 a tubular enclosure 20 extends from the frame toenclose the splined end of shaft 38 during displacement, and a suitablesheet metal cover 20a secured to the frame as by screws 20b extends overthe upper part of the pulley.

The foregoing drive structure is essentially duplicated for drivingpulley 61 at the other end of the support structure.

Housing carrier 22, like carrier 23, is slidably mounted on the machineframe guide rails 52 and 53 which are in parallel alignment with rails29 and 31, and displacement of carrier 22 is controlled by parallelcylinders 54 and 55 connected by piston rods 56 and 57 respectively tohousing 51. A shaft 58 having a splined section 59 axially slidablyextending through a pulley 61 extends into the bearing unit cartridge 62to be connected, as will appear, to rotate workpiece 11.

Pulley 61 is rotatably mounted and confined against axial displacementon a fixed sleeve 60 in the same manner that pulley 40 is mounted onsleeve 40a. Pulley 61 is non-rotatably drive connected to shaft 58through the splined drive connection provided by section 59 and drivecollar 60a. Shaft splines 59 are slidable through the splined hub ofcollar 60a during operation so that drive to the pulley is notinterrupted as carrier 62 moves along the support structure. Pulley 61is connected by belt 63 to an idler pulley 64. Pulley 64 is mounted onan idler shaft 64a which is suitably journalled for rotation about anaxis extending parallel to and vertically below shaft 58. A furtherpulley 64b, which is mounted on shaft 64a, is connected by a belt 64c toa pulley 64d. Pulley 64d is mounted 'on an output shaft 65 of anindependent power unit 66 that comprises an electric motor 67 connectedto shaft 65 through a clutch 68 and having a braking unit associatedtherewith at 69.

The hydrostatic bearing unit cartridges 37 and 62 are preferably exactlyalike, and similar reference numerals will be used for both. FIG. 3shows internal details wherein the cartridge unit comprises a housing 71that has a cylindrical periphery fitted snugly within the innerperiphery 72 of frame 51. A series of machine screws 73 extend through aradial housing flange 74 to fix housing 71 to frame 51. A forwardlyextending hollow conical nose portion 75 of the housing is secured tothe housing by a row of screws 76 at flange 74.

Housing 71 is formed with a forwardly open relatively large diameterrecess 77, and recess 77 is provided front and rear with axially spacedconcentric cylindrical surfaces 78 and 79, surface 78 near the bottom ofthe recess being of slightly smaller diameter. Concentric with recess 77is a smaller diameter bore 81 through rear wall 82 of the housing.

Within recess 77 a housing core section 83 is secured as by a series ofmachine screws 84 extending through wall 82. Core 83 is formed withcylindrical end surfaces 85 and 86 fitting snugly with recess surfaces78 and 79 respectively, and resilient seal ring and groove arrangementsindicated at 87 and 88 respectively provide static seals, wherebyinteriorly of the housing 71 an annular chamber 89 is defined betweencore 83 and the surrounding housing portion.

As will appear core 83 is formed with special lubricant distributionpassages. It is preferably made as a physically separate part from thehousing to permit the forming therein of such passages without undulycomplex casting or machining operations, but once in place as shown inFIG. 3 it becomes essentially a unitary part of housing 71.

Power driven shaft 58 is connected to a coupling 91 which is secured tothe end of a drive sleeve 92 by bolts 93. Sleeve 92 is non-rotatablymounted, as by splines at 94, on the end of a hollow arbor assembly 95.Arbor assembly 95 comprises a rear section 96 having a cylindricalsurface 97 passing through a surrounding cylindrical bore 98 in core 83,a radially enlarged flange section 99 adjacent the flat front core face100 which is perpendicular to the arbor axis, and a forward section 101having an internal cylindrical bore 102 and an outer cylin dricalperiphery 103 surrounded by a cylindrical bore 104 on the front end ofthe housing nose 75.

As will appear the arbor assembly is radially supported within thehousing on hydrostatic bearing means effective between arbor section 96and bore 98 and between arbor section 101 and bore 104.

Arbor section 96 is enlarged internally at 105 to form a cylinderchamber 106 within which a piston 107 is slidably mounted. A compressionspring 112 reacts between a radial wall 113 within the arbor and piston107 to urge the piston to the right in FIG. 3.

A piston rod 114 fixed to piston 107 extends slidably through a cap 1 15secured as by screws 116 to the flange section of the arbor to otherwiseclose the forward end of chamber 106. A suitable sealed bearing assemblyindicated at 117 permits free sliding of rod 114 while maintaining fluidpressure in chamber 106. A spacer sleeve on rod 114 limits forwarddisplacement of piston 107.

At its forward end piston rod 114 is secured to a swivel coupling 1 18peripherally engaged in internal annular grooves 1 19 on the rear end ofa series of chuck elements 121 which in turn are axially slidablymounted on a chuck element 122 fixed as by screws 123 upon the arborassembly. There are usually several chuck elements 121 equallycircumferentially distributed about the workpiece.

The forward end of each chuck element 121 has an inner workpieceengaging surface 124 and an external generally conical contour forwardinclined surface 125 that slidably engages a similarly inclined surface126 on fixed clutch element 122. Fixed clutch element 122 has aninternal annular workpiece engaging surface at 127, and a series ofcircumferentially spaced internal workpiece engaging surfaces 128between which extend the movable chuck elements 121.

The chuck arrangement and structure shown in FIG. 3 is for holding axlespindles of the shape illustrated. The invention contemplates anyequivalent chuck arrangement suited to the workpieces being welded.

In FIG. 3, piston 107 is shown displaced to its rearmost position byfluid pressure in chamber 106, and in that position it has displacedchuck elements 121 to the left whereby they ride up cam surfaces 126. tocontract the chuck and peripherally grip workpiece 11 to lock itnon-rotatably to the arbor assembly 95 concentrically on the axis ofrotation of the arbor assembly. This condition exists during thefriction welding operation as will appear.

The rear end of housing bore 81 contains a ring 131 the intemalperiphery 132 of which has free running clearance with the arbor. Collar131 is secured to the housing as by screws 133 and mounts an annularaxially resilient seal assembly 134 axially disposed between thestationary housing and the rotating arbor assembly. Thus no lubricantcan escape axially through housing bore 81.

At the front end of the cartridge, housing member 75 terminates in boss135 having a cylindrical bore 136 snugly receiving the cylindricalsurface 137 of a bearing collar 138 secured to the housing as by screws139. Bore 104 is formed on the inner periphery of collar 138. Staticseal rings 139 and 141 are provided between surfaces 136 and 137.

At its forward end a ring 142 secured to collar 138 as by screws 143mounts an axially resilient seal assembly 144 axially disposed betweenthe stationary housing structure and the rotating arbor assembly. Thusno lubricant can escape through the front end of the housing.

Seals 134 and 144 are the only two seals neededbetween the arborassembly and the housing in the novel structure of the invention.

An annular groove 151 is provided in surface 136 axially between theseal rings 139 and 141, and a radial inlet passage 152 extends outwardlyfrom this groove to connect with a supply conduit 153. Referring toFIGS. 3 and 4, it will be seen thatthe internal surface 104 of bearingcollar 138 is formed with an equally circumferentially spaced series ofcavities 154 of the same size, and each cavity is connected to groove151 by a radial passage 155 containing a sharp-edged calibrated, flowrestricting orifice 157 of predetermined size. Each orifice 157, as bestshown in FIG. 4A, is defined by a thin orifice disc 157a which is heldin place within a diametrically enlarged section of passage 155 by anannular fitting 156. Fitting 156 is threaded into the enlarged sectionof passage 155 as shown.

The diameter of cylindrical surface 104 is accurately machined a smallamount larger than the diameter of cylindrical arbor surface 103.

Oil under high pressure enters passage 152 and distributescircumferentially around groove 151 from whence it is directed intocavities 154 through the restricted orifices 157. Cavities 154 thereforeare filled with the oil at a lower pressure than the supply pressure,and the difierence in diameters of surfaces 103 and 104 provides gapsindicated at 158 (FIG. 3) and 158a (FIG. 4). Gaps 158a are delimited bythe portions of-surfaces 104 indicated at 104a and extendcircumferentially between the adjacent cavities. Normally no oil flowsthrough gaps 158a because the pressure of oil in adjacent cavities issubstantially equal during normal operation. As shown in FIG. 3, gaps158 extend axially, and cavity oil leaking laterally through these gaps158 flows directly and through drain holes 160 to enter a low-pressurespace 161 within the housing. From space 161, oil flows through passage162 back to the sump. The external oil circuit will be described inconnection with FIG. 6.

Thus, with the arbor assembly rotating about its axis indicated at 159,its forward end is radially supported by the high-pressure oilcirculating in the cavities 154 and gaps 158 and there is no metal tometal contact at surfaces 103 and 104. The foregoing constitutes thefront hydrostatic journal bearing in the assembly.

In practice the radial depth of cavities 154 and 163 should be about50-100 or more the film thickness at gaps 158 and 166 to provide aminimum loss in friction horse power. It is, of course, important tofilter the recirculated oil, as to prevent obstructions in the orificesat the cavities, and temperature control is usually provided to assurethat the oil remains within reasonable viscosity limits. Also the gaps158 and 166 usually range between 0.001 and 0.010 inch in thickness andare selected to meet requirements of the application. In thisembodiment, 0.002 inch thickness has been selected.

Referring to FIGS. 3 and 5, an oil supply conduit 161' enters a housingpassage 162' opening into chamber 89. The housing core 83 (FIG. 5) isformed around its internal periphery with a series of spaced cavities163 each of which is connected to chamber 89 by calibrated accuratelysized, restricted sharp-edged orifices 165. Orifices 165 each may bedefined by an orifice disc 164 which is held in place by a fitting in amanner similar to that described for orifice 157. Cavities 163 are thesame size and equally spaced around the surface 98.

Cylindrical surface 97 is of slightly smaller diameter than internalcylindrical surface 98 of the housing core. The incoming oil maintainshigh pressure in cavities 163 to provide balanced support of the arborduring rotation. The gaps 166 that exist between concentric surfaces 97and 98 provide relief passages between the cavities and at the sides asindicated in FIG. 3 to discharge oil into a core passage 167 throughwhich oil flows back to the sump. Communication between passage 167 andchamber 89 is blocked by plug 168.

The foregoing provides a second hydrostatic journal bearing for thearbor assembly. 7

As shown in FIG. 3, chamber 89 is connected by a core passage 171 to anannular recess 172 in surface 98, and oil from recess 172 flows througha plurality of openings 173 in the arbor to enter piston cylinder 106.Oil under pressure in cylinder 106 forces piston 107 to the left to itsworkpiece clamping position. Thus oil in the bearing assembly circuitmust be pressurized before the workpiece -11 can be securednon-rotatably to the arbor.

An oil supply conduit 181 is connected by a core passage 182 to one endof a conduit 183 extending longitudinally of core 83 to open into arelatively shallow annular chamber 184 defined by annular recess 185 inthe rear face of arbor flange 99 and the fiat front face of the core.Radially outwardly of chamber 184 the arbor flange is formed with anannular flat face 186 that is closely adjacent and parallel to core face100 so as to define a restricted passage gap indicated at 187 throughwhich oil from chamber 184 flows to lower pressure passage 162.

Gap 187 functions to provide a thin band of oil between surfaces 100 and186, thereby providing a rear hydrostatic thrust bearing preventingmetal to metal contact between arbor surface 186 and housing surface 100even under the very heavy axial pressures encountered during frictionwelding.

Oil under the pressure of cylinder 106 also enters a plurality of radialpassages 191, and one or moreof these passages 191 is connected by asharp-edged, calibrated orifice 192 providing a restricted entrance thatopens into an annular groove 194. Groove 194 is formed in a fixed ringblock 195 secured to the housing by screws 196. Orifice '192, as bestshown in FIG. 3A, is defined by a thin orifice disc 193 which is held inplace by an annular fitting 193a. Disc 193 is disposed in a short axialpassage 193b extending from passage 191 to face 197. Oil under pressureis thus delivered through orifice 192 to the annular interface betweenthe front surface of flange 99 and the housing and this provides a fronthydrostatic thrust bearing preventing metal to metal contact betweenflat annular face 197 on the arbor and flat face 198 on the housing.

Referring to FIG. 6, the oil sump is indicated at 201. An electric motor202 drives two similar constant or fixed displacement pumps 203 and 204to withdraw oil through conduits 205 and 206 and filters 207 and 208respectively. Pumps of this type, as is well known provide a constantrate of flow.

Pump 203 delivers oil to conduit 209 that is connected to conduit 181.Conduit 181, as shown in FIG. 3, leads into hydrostatic bearing unitcartridge 62 for supplying oil to the rear hydrostatic thrust bearingthere. Similarly, pump 204 delivers oil to conduit 211 connected to theconduit 181 leading into hydrostatic bearing cartridge 37 for supplyingoil to the rear hydrostatic thrust bearing there. Since pumps 203 and204 are of the fixed displacement type, the oil pressure at the thrustbearings will be dictated by applied load. The pressure differenceacross each thrust bearing will depend upon the applied load. Theoperating thrust bearing oil pressure operating range may vary from 50to 2,000 psi during operation.

A separate fixed displacement dual pump 212 driven by motor 202 suppliesoil to all of the hydrostatic journal bearings. Outlet conduit 214 frompump 212 delivers oil through a filter 215 -to a line 216 that connectsto both conduits 153 and 161 of both hydrostatic bearing cartridges.Conduit 214 is also connected to a pressure switch 210 which is disposedin the main control circuit for the welding apparatus, and this switchwill be open whenever the pressure in line 214 drops slightly below thedesigned operating pressure. When oil comes up to operating pressure,switch 210 is actuated to allow the welding cycle to be started.Cartridges 37 and 62 have a common drain line 217 connected to passages162 for returning oil back to the sump after-passing through the thrustand journal bearings. A heat exchanger 218 is provided in return line217 as it is preferable to cool the oil to a suitable temperature foroptimum viscosity about 1 10 F, when passing through the bearings. Acheck-valved bypass 219 is provided around the heat exchanger, and itwill permit return flow of oil should the heat exchanger become blocked.

Since pump 212 is of the fixed displacement type, it, together withrelief valve 222, provides a fixed pressure source which is controlledby valve 222, and the pressure differential across orifices 157 and willdepend upon the journal load.

A branch line 221 connected to conduit 214 is connected into a reliefvalve 222 which delivers oil from conduit 214 to line 225 leadingdirectly back to sump 201. This permits a controlled bypass circulationof oil without passing it through the journal bearings and therebymaintains the oil pressure supplied through line 214 at a predeterminedmagnitude.

As shown in FIG. 6, a four-way, solenoid-operated valve 224 is connectedin a conduit 223. Conduit 223 is connected at opposite ends to conduit225. When the solenoid of valve 224 is de-energized, as when the weldingapparatus controls are operated for starting a weld cycle, valve 224 isshifted to its illustrated position to block flow through a vent passage2240. This allows the oil pressure to build up to a higher limitunderthe control of valve 222 as compared with the limit that the oilpressure can build up to when valve 224 is shifted to the right where itallows oil to flow through passage 224a to the sump. With the solenoidenergized, relief valve 222 bypasses the discharge of pump 212 throughconduit 225 at substantially atmospheric pressure. The assembly ofvalves 222 and 224 is conventional and may be manufactured as a singleunit such as the Vickers Co. CT-06-lA-C20 valve unit. In such a valveunit the pressure in the operative vent passage connection schematicallyindicated at 2240 cooperates with an unshown pilot valve in valve 222 tocontrol the relief valve throttling action. This action and valveconstruction is more fully described in the Vickers Co. IndustrialHydraulics manual 935100 issued in 1965 by the Machine HydraulicsDivision of Vickers Co. and copyrighted by the Sperry Rand Corp. of TroyMichigan.

When the solenoid of valve 224 is de-energized, the pressure in conduit214 is allowed to build up to a sufficient magnitude to actuate switch210, allowing the welding cycle to be started. Valve 222 openssufficiently to prevent the oil pressure from exceeding a suitableoperating pressure (such as l,500 psi). When the solenoid of valve 224is energized, valve 222 operates to limit the oil pressure to a maximumpressure which is approximately zero psig and which is insufiicient toactuate switch 210.

A branch line 227 connects conduits 209 to the pump through a pressurerelief valve 228 which opens to limit the maximum pressure in conduit209 to 2,000 pounds per square inch and re-closes when the pressuredrops below that amount. Similarly, a branch line 229 connects conduit211 to a pressure relief valve 231 for the same purpose. These reliefvalves 228 and 231 may not be necessary as a practical matter in manyinstallations because of the pressure relief available at the rearhydrostatic thrust bearings where the radial faces 100 and 186 willseparate to decrease the oil pressure in inverse proportion to theapplied thrust load. Thus, the hydrostatic thrust bearing functionsautomatically as a relief valve even if relief valves 228 and 229 areomitted. However inclusion of those relief valves will prevent scoringand failure of the thrust bearing in the event its rated maximum thrustcapacity is inadvertently exceeded.

OPERATION In operation the workpiece 12 is placed in stationary cradle14 and clamped by jaws 15, 16, 18 and 19. The workpieces 1 1 and 13 areinserted into the open ends of the hydrostatic bearing cartridges,pistons 107 at this time being displaced into the forward positions asto the right in FIG. 3 by springs 112 so that chuckelements 121 havebeen forwardly displaced to loosely axially receive the workpieces. Atthis time the end faces of the workpieces to be friction welded togetherare axially aligned.

Now the control system for the welding machine is energized. This systemis disclosed and claimed in detail in my copending U.S. application Ser.No. 650,396, now US. Pat.

' No. 3,548,487, issued Dec. 22, 1970 for Method and Apparatus ForFriction Welding filed on even date herewith and no detailed referenceto it is here believed to be needed except to state that motor 202 runscontinuously during and between welding cycles and is thus operatingwhen motors 46 and 67 are started and drive connected to rotate spindlesl1 and 13 in the welding cycle.

Oil under pressure (about 1,500 psi) is delivered to line 216 andtherefrom to all four hydrostatic journal bearings. With reference toFIG. 3, the oil at line pressure from conduit 153 and passage 152 entersgroove 151 which circulates it to simultaneously pass through therestricted orifices 157 into cavities 154, so that all six cavities 154solidly contain bodies 104 of the housing. The equal pressure areas atthe cavities cooperate to automatically center the arbor assembly on itsaxis of rotation, and the arrangement prevents increasing radial loadson the arbor assembly from causing metal to metal contact between thearbor assembly and housing. For example, should the radial load on thearbor assembly increase at the top in FIG. 4, this will result in thearbor assembly being displaced downwardly which will reduce theseparation of surfaces 103 and 104 at the lower gaps 158 and increasethe separation of those surfaces at the upper gaps. As a consequence therelief through gaps 158 between the lower cavities will be restricted toresult in the oil pressure in the adjacent cavities increasing, and thewidened upper gaps 158 permit increased relief and therefore lower. oilpressure in the upper cavities. This condition prevails as long as thereis an unbalanced load on the bearing. The increase in oil pressure, 7

as at the bottom cavities in the foregoing example, when algebraicallyadded to the decrease in oil pressure at the upper cavities will equalthe applied load. The foregoing action is rendered possible due to theprovision of the restricted ori-- fices through which oil enters thecavities as these orifices isolate the cavities from the pressurizedsource sufficiently to enable compensation to take place. When the arborassembly becomes centered on the axis of rotation, all cavities areequally pressurized.

Oil from lines 216 and 161' enters passage 162 to provide an annularbody of oil in chamber 89 at pump pressure, and this chambersimultaneously supplies oil through all of the restricted orifices 165into the cavities 163, whereby these cavities contain oil under pressureand are interconnected by circumferential gaps 166a (FIG. 5). Surfaces97 and 98 are automatically maintained against metal to metal contact asdescribed for the front bearing. Oil from cavities 163 continuouslyflows through the sides of gaps 166 to the drain passage 162.

Thus it will be seen that the entire arbor assembly is radiallysupported and automatically centered by the front and rear hydrostaticjournal bearings in each cartridge. The combination of hydrostaticjournal bearings with the components of a machine subject to suchexceptionally large loads as friction welding apparatus is particularlynovel and useful, because bearings of the usual tapered roll or balltype designed to withstand equivalent forces would be exceptionallylarge and unexpectedly small dimensions and provides better practicaloperational conditions within smaller space at less expense,

and this contributes mainly to solve the problems of adapting frictionwelding to the joining of heavy large components.

Referring to FIG. 3, it will be seen that the hydrostatic journalbearings are disposed forwardly and rearwardly of the hydrostatic thrustbearings provided between the arbor asreplacement by locating the sealsat opposite ends of each carrier unit.

Since passage 171 conducts oil under pressure from chamber 89 to thecylinder 106, chuck elements 121 are displaced rearwardly in FIG. 3 toautomatically clamp the workpiece 11 fixedly to the arbor assembly onlywhen the radial bearings have been pressurized, and this takes placebefore the arbor assembly is rotated during the welding machine cycle.When the oil pressure drops in chamber 89 during the welding machinecycle, as when the solenoid for valve 224 is energized, the pressure incylinder 106 drops to allow spring 112 to push the chuck elementsforward to release the workpiece. By making core 83 as a separatehousing part for insert in the assembly, machining and other forming ofthe oil passages and surfaces therein is simplified and may be carriedout apart from the housing 71.

Pumps 203 and 204 simultaneously deliver oil through conduits 181 and183 into the rear hydrostatic thrust bearings of the respectivecartridges under a variable pressure depending upon the magnitude of theimposed thrust load. I Referring to FIG. 3, it will be seen that chamber184 contains an annular band or pad of oil, and oil from chamber 184passes continuously radially out in an annular thin layer in the gap 186between surfaces 185 and 100 to discharge into drain passage 162 whichdelivers the oil back to sump 201.

The arbor assembly 95 is so mounted in the apparatus as to have apredetermined range of controlled small axial float in the housing. Theallowable degree of float is such that, with zero thrust (no axial load)which is the condition that exists before the workpieces 11 and 13engage the ends of workpiece 12, oil pressure in chamber 184 urging thearbor assembly forwardly increases gap 187 to such width that the pumppressure falls to only about five percent of its maximum value. Thisautomatic relief means that little power is consumed and the apparatusis free of high-pressure oil strain except when actually performing thewelding operation during each cycle.

It is a noteworthy feature of the invention that the high pressure oilcircuit within each cartridge requires no oil seals within thecartridge. The only oil seals at 134 and 144 need withstand lower oilpressures.

The annular land 172a FIG. 3) in surface 98 effectively isolates therear or outboard hydrostatic journal bearing from the higher pressure,oil in the thrust bearing circuit, the space between surfaces 97 and 98extending between chamber 184 and groove 172 providing a very lowleakage seal between the two oil circuits within the cartridge.

A hydrostatic reverse thrust bearing is provided at the front side offlange section 99 of the arbor assembly, where oil at the pressure ofpiston chamber 106 is discharged through the series of circumferentiallyspaced restricted orifices 192 to throttle at lower pressure intoannular groove 194, and this lower pressure is adequate to alwaysmaintain flange section 99 of the arbor assembly from metal to metalcontact with the housing.

When the pressurized oil circuits in the radial journal bearings havebeen established, when the power units 45 and 65 are actuated to drivethe arbor assemblies, and when the arbor assemblies are up to speed, therespective" cylinders at 32 and 33 and 54 and 55 are operated to slidecarriers 22 and 23 toward each other to frictionally engage theworkpieces. Once these are engaged the journal and thrust loads,particularly the latter, increase tremendously. The automaticcompensation at the journal bearings has been above described.

As the thrust increases the entire arbor assembly will-tend to shifirearwardly relative to housing 71, to the left in FIG. 3. This does notcause any oil leakage at the end seals 134 and 144 because these sealsare axially resilient and the oil pressure there is relatively low, andseal 144 axially expands to maintain sealing engagement with thehousing. Rearward displacement of the arbor assembly results inrestriction of the annular gap 187 between the flat parallel surfaces100 and 186, to decrease the relief from chamber 184, and this resultswelding apparatus for welding spindles onto axle housings isadequate tooppose axial thrust up to 150,000 pounds at the welding joint.

The invention is particularly effective in heavy duty friction weldingapparatus wherein the welding cycle involves periods where full capacityof the thrust is developed at zero speed. The weld under the appliedaxial pressure develops immediately after rotation of the end workpieces11 and 13 is stopped. I-Iydrostaticbearings as disclosed maintainadequate film thickness layers of lubricant at the gaps 158, 166 and 187under the very heavy load low speed conditions encountered. As a resultof the pressurized oil support conditions provided by the hydrostaticbearings there is little or no bearing starting friction to overcomewhen the motors 46 and 67 are set in operation and minimum power isrequired for accelerating the rotating workpieces, and operationalspeeds are quickly attained even for such heavy masses as axle housingcomponents, which speeds operation and increases production.

It is also to be noted that the pressure of oil supplied to the thrustbearings varies with the imposed axial load from a small valueapproaching zero to a much greater value, with the upper limit beingappreciably higher than the fixed supply of pressure to the journalbearings.

As shown in FIG. 3, the front hydrostatic journal bearing defined bycavities 154 and gaps 158 circumferentially surrounds the chuck elementworkpiece gripping surfaces. This provides for'a workpiece journalsupport of appreciable hydraulic stiffness and great load carryingcapacity and minimizes the movement arm of the journal support so thatthe workpiece 11, when rotating, will not whip to any significantdegree.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent 1. Ahydrostatic bearing unit for friction welding apparatus comprising ahousing, an arbor assembly extending through said housing and havingmeans for clutching a workpiece thereto, spaced hydrostatic journalbearings rotatably mounting said arbor assembly on said housing, andmeans mounting said arbor assembly for controlled limited axial float onsaid housing comprising hydrostatic thrust bearing means comprisingopposed adjacent axial surfaces on said housing defining an annularrecess at said surfaces, means for introducing liquid under pressureinto said recess, and means defining an annular gap between saidsurfaces peripherally outwardly of, 7 said recess for restricteddischarge of liquid from said recess, one of said thrust surfaces beingsupplied with fluid from an independent fixed displacement source whilethe other of said thrust surfaces being supplied from another sourcethrough at least one compensating orifice.

2. The hydrostatic bearing unit defined in claim 1, wherein said thrustbearing means comprises a main hydrostatic thrust bearing opposing axialdisplacement of said arbor assembly during the friction weldingoperation, and a reverse thrust hydrostatic bearing opposingdisplacement of the arbor assembly in the opposite direction.

3. The hydrostatic bearing unit defined in claim 2, wherein said thrustbearings are disposed between axially spaced portions of said housingand opposite sides of a radial flange on said arbor assembly.

4. The hydrostatic bearing unit defined in claim 1, wherein each of saidjournal bearings comprises an annular housing chamber connected to asource of liquid under pressure, a circumferentially spaced plurality ofcavities in an inner cylindrical surface of said housing extendingaround a cylindrical surface on said arbor assembly, and means providinga plurality of restricted orifice passages between said chamber and allof said cavities, said surfaces being spaced as to provide restrictedgaps through which liquid is adapted to be discharged from said cavitiesat low pressure.

5. The hydrostatic bearing unit defined in claim 4, wherein said arborassembly contains a cylinder in which is slidable a piston operativelyconnected to said clutching means, and a passage from one of saidannular housing chambers to said cylinder for introducing fluid pressureinto said cylinder to displace said piston to actuate said clutchingmeans when fluid under pressure is supplied to the radial bearings.

6. The hydrostatic bearing unit defined in claim 4, wherein said thrustbearing means comprises a main hydrostatic thrust bearing between thehousing and arbor assembly and a reverse thrust hydrostatic bearingbetween the arbor assembly and the housing, means comprising at leastone calibrated orifice for introducing fluid under pressure from one ofsaid annular housing chambers into said reverse thrust bearing, andmeans for introducing fluid from a fixed displacement source into saidmain thrust bearing.

7. The hydrostatic bearing unit defined in claim 1, means providingaxially resilient seals between said arbor assembly and said housing atopposite ends of said arbor assembly for maintaining fluid tight sealingof said arbor assembly with said housing regardless of axial shift ofsaid arbor assembly.

8. The hydrostatic bearing unit defined in claim 1, wherein said housingcomprises an outer part formed with a recess open at one side, an insertcore fixed in said recess and formed with a peripheral groove to providean annular chamber within the housing, said core having a cylindricalsurface closely surrounding a cylindrical surface on the arbor assemblyand there being a plurality of cavities circumferentially distributedabout said core surface and a corresponding plurality of restrictedorifices connecting said chamber to said cavities, a flange on saidarbor assembly having on one side a recessed surface facing an end ofsaid insert core and parallel annular surfaces on said core and flangeperipherally outwardly of the recess in said flange surface defining arestricted gap through which fluid is discharged from said recess todefine a main hydrostatic thrust bearing, and a thrust bearing betweenthe other side of said flange and an adjacent part of the housing.

9. A hydrostatic bearing system for an axially displaceable,housing-mounted member comprising first and second hydrostatic thrustbearing means for respectively absorbing loads applied in axiallyopposite directions with respect to said member, fixed displacement pumpmeans providing a first source for supplying hydraulic fluid at asubstantially constant flow rate to said first bearing means regardlessof the magnitude of the load imposed thereon, means independent of thefluid supplied by said first source for providing a substantiallyconstant pressure hydraulic fluid source and means including orificemeans providing fluid communication between said constant pressurehydraulic fluid source and said second bearing means to deliverhydraulic fluid to said second bearing means.

10. The hydrostatic bearing system defined in claim 9 comprisinghydrostatic journal bearing means for rotatably supporting said member,and further fixed displacement pump means supplying hydraulic fluid tosaid journal bearing means and providing said constant pressurehydraulic fluid source.

1. A hydrostatic bearing unit for friction welding apparatus comprisinga housing, an arbor assembly extending through said housing and havingmeans for clutching a workpiece thereto, spaced hydrostatic journalbearings rotatably mounting said arbor assembly on said housing, andmeans mounting said arbor assembly for controlled limited axial float onsaid housing comprising hydrostatic thrust bearing means comprisingopposed adjacent axial surfaces on said housing defining an annularrecess at said surfaces, means for introducing liquid under pressureinto said recess, and means defining an annular gap between saidsurfaces peripherally outwardly of said recess for restricted dischargeof liquid from said recess, one of said thrust surfaces being suppliedwith fluid from an independent fixed displacement source while the otherof said thrust surfaces being supplied from another source through atleast one compensating orifice.
 2. The hydrostatic bearing unit definedin claim 1, wherein said thrust bearing means comprises a mainhydrostatic thrust bearing opposing axial displacement of said arborassembly during the friction welding operation, and a reverse thrusthydrostatic bearing opposing displacement of the arbor assembly in theopposite direction.
 3. The hydrostatic bearing unit defined in claim 2,wherein said thrust bearings are disposed between axially spacedportions of said housing and opposite sides of a radial flange on saidarbor assembly.
 4. The hydrostatic bearing unit defined in claim 1,wherein each of said journal bearings comprises an annular housingchamber connected to a source of liquid under pressure, acircumferentially spaced plurality of cavities in an inner cylindricalsurface of said housing extending around a cylindrical surface on saidarbor assembly, and means providing a plurality of restricted orificepassages between said chamber and all of said cavities, said surfacesbeing spaced as to provide restricted gaps through Which liquid isadapted to be discharged from said cavities at low pressure.
 5. Thehydrostatic bearing unit defined in claim 4, wherein said arbor assemblycontains a cylinder in which is slidable a piston operatively connectedto said clutching means, and a passage from one of said annular housingchambers to said cylinder for introducing fluid pressure into saidcylinder to displace said piston to actuate said clutching means whenfluid under pressure is supplied to the radial bearings.
 6. Thehydrostatic bearing unit defined in claim 4, wherein said thrust bearingmeans comprises a main hydrostatic thrust bearing between the housingand arbor assembly and a reverse thrust hydrostatic bearing between thearbor assembly and the housing, means comprising at least one calibratedorifice for introducing fluid under pressure from one of said annularhousing chambers into said reverse thrust bearing, and means forintroducing fluid from a fixed displacement source into said main thrustbearing.
 7. The hydrostatic bearing unit defined in claim 1, meansproviding axially resilient seals between said arbor assembly and saidhousing at opposite ends of said arbor assembly for maintaining fluidtight sealing of said arbor assembly with said housing regardless ofaxial shift of said arbor assembly.
 8. The hydrostatic bearing unitdefined in claim 1, wherein said housing comprises an outer part formedwith a recess open at one side, an insert core fixed in said recess andformed with a peripheral groove to provide an annular chamber within thehousing, said core having a cylindrical surface closely surrounding acylindrical surface on the arbor assembly and there being a plurality ofcavities circumferentially distributed about said core surface and acorresponding plurality of restricted orifices connecting said chamberto said cavities, a flange on said arbor assembly having on one side arecessed surface facing an end of said insert core and parallel annularsurfaces on said core and flange peripherally outwardly of the recess insaid flange surface defining a restricted gap through which fluid isdischarged from said recess to define a main hydrostatic thrust bearing,and a thrust bearing between the other side of said flange and anadjacent part of the housing.
 9. A hydrostatic bearing system for anaxially displaceable, housing-mounted member comprising first and secondhydrostatic thrust bearing means for respectively absorbing loadsapplied in axially opposite directions with respect to said member,fixed displacement pump means providing a first source for supplyinghydraulic fluid at a substantially constant flow rate to said firstbearing means regardless of the magnitude of the load imposed thereon,means independent of the fluid supplied by said first source forproviding a substantially constant pressure hydraulic fluid source andmeans including orifice means providing fluid communication between saidconstant pressure hydraulic fluid source and said second bearing meansto deliver hydraulic fluid to said second bearing means.
 10. Thehydrostatic bearing system defined in claim 9 comprising hydrostaticjournal bearing means for rotatably supporting said member, and furtherfixed displacement pump means supplying hydraulic fluid to said journalbearing means and providing said constant pressure hydraulic fluidsource.